The object of the invention relates to a method and a device for determining the quality of milk, in particular in machine milking. Raw milk is a principal raw material for the food industry and important as food. For the protection of consumers and to ensure technical processability, raw milk must satisfy both national and international quality requirements.
According to §3 of the Ordinance on Hygiene and Quality Requirements for Milk and Milk Products based on milk (Ordinance on milk in the Federal Republic of Germany), raw milk must not show anomalous sensory characteristics, such that according to Annex 3 of the Ordinance on milk, persons who milk animals must separately milk the first jets of milk from each teat so as to verify the perfect quality by inspecting the appearance of the milk of each animal. According to §18 para. 1 No. 1 of the Ordinance on milk the first jets of milk must not be placed on the market as foodstuff.
Animals whose milk is extracted as foodstuff must not suffer from recognizable udder inflammation according to Annex 1 of the Ordinance on milk. Corresponding legislation (Council Directive 92/46 EEC, Annex A and Council Directive 89/362 EEC, Annex Chapter III) is applicable within the European Union.
An indication of recognizable udder inflammation—clinical mastitis—is among other things the presence of clots in the milk yield from individual gland complexes, udder quarters or udder halves and in the entire milk yield of any individual animal. Such clots may consist of tissue residue, vibrio, cell detritus, blood coagula, and mastitis pathogens.
It is known that the size of macroscopic, detectable clots ranges from 100 μm to several millimeters. Accumulated clots in specific milk yield fractions, primarily the foremilk and first milk, may result in a highly viscous secretion with particles of several millimeters in diameter. Such clots are critical particles as regards quality since they determine and may even prohibit marketability of raw milk.
Apart from clots, foremilk and first milk may comprise particles not indicative of a recognizable udder inflammation but foreign matter from the ambience. The reason that such particles enter the foremilk and first milk may be inadequate cleaning of the animal udder or reattaching the milking unit after it was kicked off. Such particles include for example wood chips, straw particles, hair, hay, sand, bedding, and feces.
In conventional milking technology, milk collection pieces tend to be used from which the milk is routed in a long milk hose through a milk line to a bulk milk tank where it is cooled and stored. The milk is then processed further in specialist works. Automatic milking installations (AMI) are typically not equipped with short milk hoses and a milk collection piece, such that the milk is routed from the teat cups in separate milk hoses to the milk line and finally, collected, cooled and stored in a bulk milk tank.
The milk yields from multiple animals milked concurrently will commingle in the milk line. The bulk milk tank receives all of the milk yield of the animals in a dairy animal farm which collected milk is called herd bulk milk.
Under the directives of the Ordinance on milk any animals with recognizable udder inflammation must be milked separately where conventional milking technology provides that between the long milk hose and the junction into the milk line a collecting container is installed into which the milk of such animals is fed. This milk yield will then be discarded. The decision whether or not milk is obviously different from what it should be is based on prior inspection by the milker of the appearance of the separately extracted foremilk.
In practice, however, there is the risk that the visual characteristics check will often be skipped since it is in general time-demanding and thus uneconomic. Devices which allow the trapping of clots must be checked by the milker which is also very time-demanding.
Automatic and robot-assisted milking installations do not allow any visual inspection of the separately extracted foremilk by a person. The technical devices and methods thus far known operate inadequately such that there is no guarantee that milk extracted in automatic milking will satisfy national and international quality requirements.
Different methods and devices are known for determining particles in milk. The U.S. Pat. No. 4,376,053 for example proposes a filter unit comprising a filter casing having an outwardly open slot. The filter casing carries a filter element that is supported by a sealing means in a fitted frame. For visual inspection of the milk yield for any particles the filter element is removed from the filter housing and visually inspected. To avoid clogging of the milk line through the filter element which may cause the vacuum at the milking unit to drop which may in turn cause the milking units to fall off, a by-pass is provided parallel to the milk flow path.
In WO 00/67559 an apparatus for the automatic selecting out of milk during machine milking is depicted. This device comprises a measuring device for monitoring the extracted milk. An inspection of the particles deposited on a filter is carried out by detection through a detector means. It is proposed to perform particle detection by measuring the loss of intensity in radiation through the filter element, i.e. in transmission. There is also the option to measure the quantity of deposited particles by measuring the reflected intensity. To verify the presence of particles exceeding a predetermined extent, WO 00/67559 proposes that radiation be emitted substantially parallel to the filter surface. A suitable selection of the distance of the radiation source and the receiver from the filter surface allows to determine the extent of the particles in a plane. To obtain information on the particle sizes it is also proposed to equip the filter element with electrically conductive elements distanced and insulated from one another. If current or voltage is applied to these elements, the quantity of particles present on the filter surface can be established. This would require that the resistance ratio changes in relation to the deposited particles.
This approach is not without problems since the electrical conductivity of the milk is different for each animal. The electrical conductivity can also change in the course of the lactation period. The nutrition of the animals will also influence the physical characteristics of raw milk. Electrically non-conductive particles cannot be detected unless they are moistened by a conductive liquid (milk, water) but then the milk conductivity will be measured for electrically non-conductive particles and no further details on the particle are obtained.
The clots or particles must be determined for each individual animal. This requires that the filter element can be reliably and safely cleaned without the risk of contaminating subsequent milk streams with particles from previous milk yields. In the apparatus known from WO 00/67559 the filter element is cleaned in that the particles deposited on the filter element are washed out with the aid of the milk stream when the filter element is turned. Alternatively, “back splash” cleaning of the filter element may be employed. This involves the risk that particles from the subsequent milk stream may be deposited on the edge face of the filter element which may result in incorrect measuring. There is also the risk that particle-free milk streams are contaminated with quality-diminishing particles from previous milk yields.
Since crucial criteria for a perfect quality of milk include not only an absence of particles but in particular an absence of clots—because clot-containing milk indicates an udder inflammation which would prohibit that it enter the food chain—it is imperative to recognize and separate clot-containing milk. In addition to the prior art described in WO 00/67559, EP 1 126 757 B1 and DE 101 31 781 C1 have disclosed other devices and methods for examining milk for particles. The mere detection of particles is, however, not sufficient for determining the quality of milk since a checking for the presence of particles may degrade good quality milk as clot-containing milk if foreign matter such as straw, sand, . . . have entered it. This cannot be entirely excluded even after cleaning the udder since cleaning may have been performed inadequately or improperly. It is readily possible that air bubbles or foam are identified as particles. Conventional devices and methods do not allow a distinction.